Views: 0 Author: Site Editor Publish Time: 2026-10-05 Origin: Site
Ice flashover on transmission line insulators remains one of the most severe threats to power grid reliability in cold climate regions. Glaze icing forms icicles along insulator surfaces that bridge adjacent sheds, drastically shortening the effective creepage distance and ultimately triggering flashover at normal service voltage. The phenomenon is further aggravated by the crystallisation effect during phase transition, in which conductive ions are expelled from the ice lattice and accumulate on the ice–air interface, increasing surface water film conductivity by 5–10 times compared to the original pollution layer. Conventional mitigation measures—such as increasing string length or applying PRTV coatings—have shown limited effectiveness, with PRTV even reducing icing flashover voltage by 10–15%. This has driven growing interest in integrated strategies that combine shed profile optimization with advanced anti-icing coatings to achieve complementary protection.
Under simultaneous pollution and ice accretion, flashover behaviour deviates fundamentally from standard pollution flashover models. Three phenomena dominate: ice bridging across inter-shed gaps, pollution migration to the ice surface during freezing, and erratic arc propagation that jumps across partially melted ice segments. The partial arc of an iced insulator string is initiated by breakdown of air gaps between icicle tips and the iced insulator surface, and its persistence is considerably longer than that of a polluted insulator string. These characteristics make ice flashover particularly difficult to predict and suppress through conventional design margins alone.
Shed configuration is a decisive factor influencing an insulator's icing flashover voltage. Systematic energized icing tests at 35 kV and 110 kV have demonstrated remarkable differences in flashover performance among insulators of identical voltage grade but different shed geometries. Numerical simulation of icicle growth has revealed that the number of booster sheds has an optimized range, and saturated icicle bridged degree of large sheds can serve as a characterization parameter for ice flashover voltage.
Natural icing tests conducted at the Xuefengshan icing test station have produced specific design guidelines. The top surface inclination should be appropriately increased, shed spacing should exceed 40 mm, and at least three middle or small sheds should be placed between adjacent large sheds. An optimal arrangement follows the pattern of "large-small-middle-small-middle-small-large," with shed diameters preferably set at 250/150/90 mm. Comparative studies have confirmed that insulators employing anti-icing shed types achieve flashover voltage gradients of 61.0–69.4 kV/m, representing a 12–27% improvement over ordinary shed configurations. The V-type and inverted V-type string arrangements, combined with large–small diameter alternating shed arrangements, further enhance icing flashover voltage by approximately 15–20%.
Superhydrophobic coatings offer a complementary defence by modifying the surface wettability of insulator sheds. By combining low surface energy with micro/nanoscale hierarchical structures, these coatings cause water droplets to bead and roll off before freezing can occur. A regenerative superhydrophobic coating based on PDMS-modified silica nanoparticles within an F-POSS matrix achieved a static contact angle of 169.5° and ice adhesion as low as 71.2 kPa, with the coating exhibiting a higher flashover voltage than uncoated reference samples and maintaining minimal degradation after consecutive icing/de-icing cycles.
Environmental durability remains a critical concern for outdoor applications. PTFE/SiO₂-ER/FR composite superhydrophobic coatings have demonstrated robust performance, maintaining a contact angle above 150° after 66 days of UV irradiation and stabilising at approximately 157° after 26 freeze–thaw cycles. Under natural icing conditions, coated insulators exhibited a 14.2% reduction in ultimate ice accumulation and a 67.7% reduction in maximum ice ridge length compared to uncoated units. Multifunctional nano-coatings applied to silicone rubber have increased wet flashover voltage by up to 60% relative to pristine silicone rubber, while reducing de-icing force and inhibiting electrical field distortion.
The most compelling results emerge when optimized shed geometry and anti-icing coatings are deployed together. Experimental studies combining an aerodynamic-tilted shed design (Type C) with superhydrophobic coating (C3) under severe icing and pollution conditions achieved a flashover voltage of 71 kV, approaching 78% of dry-state performance—a 2.5× improvement over standard insulators. This synergy arises from complementary mechanisms: the optimized shed geometry physically impedes icicle bridging across inter-shed gaps, while the superhydrophobic coating delays ice nucleation and reduces adhesion strength at the ice–surface interface. Together, they preserve effective creepage distance and suppress the formation of the continuous conductive water film that initiates flashover.
The combined approach also addresses the long-term reliability concerns associated with coatings alone. Even if the superhydrophobic surface undergoes partial degradation after years of UV exposure and freeze–thaw cycling, the underlying shed geometry continues to provide baseline anti-icing protection. This layered defence strategy reduces dependence on any single mitigation method and improves the overall reliability of the insulation system.
Several challenges must be addressed before integrated solutions can achieve widespread field deployment. The mechanical robustness of superhydrophobic coatings remains a limiting factor, as even slight abrasion and vibration may compromise the micro/nanostructured surface. Regenerative coating systems capable of regaining superhydrophobicity after degradation represent a promising pathway to extend service life. From an engineering economics perspective, large-area and rapid spraying technologies for transmission line applications need further development to form long-term, durable, and wear-resistant coatings. Standardised test protocols, based on existing IEEE and IEC frameworks for insulator icing evaluation, will also be essential for comparing and validating different combined strategies.
Ice flashover prevention on transmission line insulators demands solutions that address both the geometric and surface-level mechanisms of ice accumulation. Shed profile optimization—through increased top surface inclination, controlled shed spacing, and large–small diameter alternating arrangements—provides baseline geometric protection against icicle bridging. Anti-icing coatings with superhydrophobic properties complement this by delaying ice nucleation and reducing ice adhesion. When deployed synergistically, these strategies deliver substantially greater flashover voltage retention under severe icing conditions than either approach alone. As regenerative coating technologies mature and standardised evaluation methods emerge, integrated shed-coating solutions are positioned to become the preferred design philosophy for insulators operating in high-altitude icing regions.
